X-Ray Fluorescence is an elemental method that relies on the fluorescence of atoms when excited by x-rays, with the detection of the emitted photons allowing qualitative and quantitative analysis of the sample.
Portable, handheld XRF units are available for heavy metal screening and detection in soil.
Only suited to heavy elements.
Commercial.
Some comprehensive overviews of of XRF for environmental analysis [1].
1. Kalnicky, D., Singhvi, R., 2001. Field portable XRF analysis of environmental samples. Journal of Hazardous Materials. 83, 93-122.